The invention relates to a starting/driving unit for an internal combustion engine of a motor vehicle, having at least two starting methods, having a clutch between the crankshaft, the engine, and the vehicle transmission, and also having an electric machine which is connected directly to the engine and/or the clutch is connected to the engine.
A starting/driving unit of this kind for two starting methods has been disclosed by DE 197 05 610 A1. In this connection, the starting method is chosen as a function of the temperature of the engine. The starting methods require two starting systems. The electric machine that serves as a motor and generator is used to start the warm engine while a conventional starter, together with electric machine, is used for starting when the engine is cold. The two starting systems require a high expenditure in order to also be able to function in stop-and-start operation and in inertial system operation.
Conventional starters have disadvantages for a number of reasons. In terms of the service life of the starter motor, in terms of the service life of the pinion and the toothed ring as well as the override clutch, and in terms of noise generation, starters of this kind do not attain the goal if the number of starting cycles is increased due to repeated starts when the engine is warm, e.g. in stop-and-start operation at traffic signals, in traffic jams, or after a thrust phase, in which a faster and quieter start is required. Even if the starter is provided with improved electronics, which results in an increased starting cycle count, this is not sufficient to achieve required starting cycle counts of &gt;200,000. The starting system that is improved in this manner cannot achieve the desired starting time and quietness.
In addition, WO 98/05882 has already disclosed providing a starting generator for direct starting. This embodiment cannot be realized with a conventional 12 V to 24 V lead starter battery because of the starting energy and the starting output during a cold start. Furthermore, the electric motor would have to be enlarged by more than a factor of 3 in relation to the demand for the generator output, which among other things, can also lead to difficulties with the structural size. However, extremely high starting moments and battery outputs are not required in order to start the warm engine.
The use of a starting generator for an impulse start according to DE 197 45 995 A1, in which a starting generator is connected to the crankshaft by way of a start coupling between the crankshaft and a flywheel in addition to or in lieu of the usual coupling between the flywheel and the vehicle transmission, functions so that when the engine (and transmission) are uncoupled, the electric motor first accelerates the flywheel mass to the drive speed (e.g. 1000 rpm) and then with a rapidly following start coupling or clutching, drives the engine via the rotation energy. This impulse start is suitable for normal cold starts, but due to time constraints, is unfavorable for re-starting when the engine is warm both at traffic signals and after the end of thrust phases.